LOW NOx BURNER APPARATUS AND METHOD

ABSTRACT

A burner apparatus for a fired-heater system and a method of burner operation wherein the burner fuel is ejected outside of the burner wall from a surrounding fuel discharge ring, or from a lateral elongate ejection bar in the case of a flat flame burner, to a combustion zone projecting from the forward end of burner wall. The burner apparatus and method reduce NO x  production by a combination of enhanced internal flue gas recirculation and staged fuel operation.

FIELD OF THE INVENTION

The present invention relates to burner assemblies and to methods and apparatuses for reducing NO_(x) emissions from burners of the type used in process heaters, boilers, furnaces and other fired heating systems.

BACKGROUND OF THE INVENTION

Many industrial applications require large scale generation of heat from burners for process heaters, boilers, furnaces, or other fired heating systems. If the burner fuel is thoroughly mixed with air and combustion occurs under ideal conditions, the resulting combustion products are primarily carbon dioxide and water vapor. However, when the fuel is burned under less than ideal conditions, e.g., at a high flame temperature, nitrogen present in the combustion air reacts with oxygen to produce nitrogen oxides (NO_(x)). Other conditions being equal, NO_(x) production increases as the temperature of the combustion process increases. NO_(x) emissions are generally considered to contribute to ozone depletion, acid rain, smog, and other environmental problems.

For gaseous fuels with no fuel bound nitrogen, thermal NO_(x) is the primary mechanism of NO_(x) production. Thermal NO_(x) is produced when the flame reaches a high enough temperature to break the covalent N₂ bond so that the resulting “free” nitrogen atoms then bond with oxygen to form NO_(x).

Typically, the temperature of combustion is not great enough to break all of the N₂ bonds. Rather, most of the nitrogen in the air stream passes through the combustion process and remains as diatomic nitrogen (N₂) in the combustion products. However, some of the N₂ will typically reach a high enough temperature in the high intensity regions of the flame to break the N₂ bond and form “free” nitrogen. Once the covalent nitrogen bond is broken, the “free” nitrogen is available to bond with other atoms. Fortunately, the free nitrogen will most likely react with other free nitrogen atoms to form N₂. However, if another free nitrogen atom is not available, the free nitrogen will react with oxygen to form NO_(x).

As the temperature of the burner flame increases, the stability of the N₂ covalent bond decreases, causing increasing production of free nitrogen and thus also increasing the production of thermal NO emissions. Consequently, in an ongoing effort to reduce NO emissions, various types of burner designs and theories have been developed with the objective of reducing the peak flame temperature.

The varied requirements of refining and petrochemical processes necessitate the use of numerous different types and configurations of burners. The approaches used to lower NO_(x) emissions can differ from application to application. However, thermal NO reduction is generally achieved by slowing the rate of combustion. Since the combustion process is a reaction between oxygen and the burner fuel, the objective of delayed combustion is typically to reduce the rate at which the fuel and oxygen mix together and burn. The faster the oxygen and the fuel mix together, the faster the rate of combustion and the higher the peak flame temperature.

Examples of different types of burner design approaches used for reducing NO_(x) emissions have included:

-   -   a. Staged air designs wherein the combustion air is typically         separated into two or more flows to create separate zones of         lean and rich combustion.     -   b. Designs using Internal Flue Gas Recirculation (IFGR) wherein         some of the burner fuel passes through and mixes with the inert         products of combustion (flue gas) in the combustion system to         form a diluted fuel which burns at a lower peak flame         temperature.     -   c. Staged fuel designs wherein the fuel is separated into two or         more flows to create separate zones of lean and rich combustion.     -   d. Designs using External Flue Gas Recirculation (EFGR) wherein         inert products of combustion are mixed with the combustion air         to reduce the oxygen concentration of the air stream supplied to         the burner, which in turn lowers the peak flame temperature.     -   e. Designs using “flameless” combustion wherein most or all of         the burner fuel passes through and mixes with inert products of         combustion to form a diluted fuel which burns at a lower peak         flame temperature. The mixture of fuel and inert products of         combustion can be as high as 90% inert, thus resulting in a         “transparent” flame.     -   f. Designs using steam and/or inert injection into the burner         fuel wherein the steam or inert components mix with the fuel so         that the resulting composition will burn at a lower peak flame         temperature.     -   g. Designs using steam and/or inert injection into the         combustion air stream wherein the steam and/or inert components         mix with the combustion air so that the resulting composition         will burn at a lower peak flame temperature.

SUMMARY OF THE INVENTION

The present invention provides a low NO_(x) burner apparatus and method which achieve further reductions in NO), emissions at lower cost, reduced complexity, and higher efficiency. The inventive burner and method provide both staged fuel operation and internal flue gas recirculation (IFGR) for lowering combustion temperatures and reducing NO_(x) emissions. In addition, the inventive burner and method allow the entire fuel stream to be conditioned with flue gas.

In contrast to prior burners which require the use of a plurality of individual ejector tips, the inventive burner and method preferably employ a single ejector ring with tip, or an elongate bar-type fuel ejector, which increases the level of IFGR provided by the burner by (a) increasing the available ejection tip area of the burner, (b) increasing the number of ejection ports which can be used, (c) allowing the ejection ports and the resulting ejection streams to be positioned much closer together, and/or (d) allowing the use of a continuous or elongated ejection slot. The inventive burner and method also provide high levels of performance in regard to flame length, available turndown ratio, and stability.

In one aspect, there is provided a burner apparatus preferably comprising: (a) a burner wall having a combustion zone projecting forwardly from or proximately from a forward end of the burner wall, wherein the burner wall surrounds a flow passageway for air or other oxygen-containing gas which extends longitudinally through the burner wall and the flow passageway has a longitudinally forward discharge opening at the forward end of said burner wall and (b) a fuel discharge ring which is positioned outside of the flow passageway and longitudinally rearward of the forward end of said burner wall for discharging a burner fuel, the fuel discharge ring substantially surrounding, laterally, the flow passageway. The fuel discharge ring preferably includes either (i) a plurality of fuel discharge openings which substantially surround the flow passageway and are positioned and oriented in a direct or angled forward direction to deliver the burner fuel outside of the burner wall to the combustion zone during operation or (ii) a single fuel discharge slot which substantially surrounds the flow passageway and is positioned and oriented in a direct or angled forward direction to deliver the burner fuel outside of the burner wall to the combustion zone during operation.

In another aspect, there is provided a burner apparatus preferably comprising: (a) a burner wall having a combustion zone projecting from or proximately from a forward end of the burner wall, wherein the burner wall surrounds a flow passageway for air or other oxygen-containing gas which extends longitudinally through the burner wall, the flow passageway has a longitudinally forward discharge opening at the forward end of the burner wall, and the flow passageway has at least one side at the forward discharge opening which is substantially flat and (b) an elongate fuel discharge conduit which extends laterally and is positioned outside of the one side of the flow passageway and longitudinally rearward of the forward end of the burner wall for discharging a burner fuel. The elongate fuel discharge conduit preferably includes either (i) a plurality of fuel discharge openings which extend along at least most of the elongate fuel discharge conduit and are positioned and oriented in a direct or angled forward direction to deliver the burner fuel outside of the burner wall to the combustion zone during operation or (ii) a single fuel discharge slot which extends along at least most of the elongate fuel discharge conduit and is positioned and oriented in a direct or angled forward direction to deliver the burner fuel outside of said burner wall to the combustion zone during operation.

In another aspect, there is provided a method of operating a burner which preferably comprises the steps of: (a) delivering an oxygen-containing gas through a flow passageway surrounded by a burner wall, wherein the burner wall has a longitudinal axis which extends through the flow passageway, the flow passageway has a longitudinally forward discharge opening at a forward end of the burner wall, and the forward end of the burner wall has an outer lateral cross-sectional shape, and (b) discharging a flow of burner fuel forwardly from a fuel discharge ring such that the flow of burner fuel is received in a combustion zone which projects forwardly from or proximately from the forward end of the burner wall. The fuel discharge ring is positioned outside of the flow passageway and longitudinally rearward of the forward end of said burner wall. The flow of burner fuel, as it is discharged from the fuel discharge ring, has a lateral cross-sectional shape which substantially surrounds the flow passageway and corresponds to the outer lateral cross-sectional shape of the forward end of the burner wall.

Further aspects, features, and advantages of the present invention will be apparent to those of ordinary skill in the art upon examining the accompanying drawings and upon reading the following Detailed Description of the Preferred Embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embodiment 10 of the inventive burner apparatus.

FIG. 2 is an elevational side view of the inventive burner apparatus 10.

FIG. 3 is a cutaway elevational side view of the inventive burner apparatus 10.

FIG. 4 is an enlarged perspective view of a portion of the inventive burner apparatus 10.

FIG. 5 is a front view of an alternative embodiment 36 of a fuel discharge ring for use in the inventive burner apparatus 10.

FIG. 6 is an elevational side view of an alternative flat-flame embodiment 100 of the inventive burner apparatus.

FIG. 7 is an elevational front view of the inventive burner apparatus 100.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment 10 of the inventive burner apparatus is illustrated in FIGS. 1-4. The inventive burner 10 preferably comprises: a housing 12 having an outlet end 14; a burner wall 16 which is positioned at the outlet end 14 of the housing 12 and has a longitudinal axis 18 which extends therethrough; an air flow passageway 22 which extends through and is surrounded by the burner wall 16 and has a longitudinally forward discharge opening 24 at the forward end 20 of the burner wall 16; a fuel discharge ring assembly 26 for ejecting a gaseous or liquid burner fuel outside of the burner wall 16 toward the forward discharge end 20 thereof; and at least one pilot burner assembly 25 which extends through the discharge section 28 of the housing 12 and into the air flow passageway 22 of the burner wall 16.

The housing 12 has a windbox or other inlet 32 upstream of the discharge section 28 for receiving combustion air or other oxygen containing gas. Combustion air (or an alternative oxygen-containing gas) is received through the inlet 32 and flows through the housing 12 to the inlet end 35 of the burner wall 16. The air (or other oxygen-containing gas) then flows through the flow passageway 22 of the burner wall 16 and exits the forward discharge opening 24 of the passageway 22. The quantity of combustion air entering housing 12 can be regulated using an inlet damper (not shown) or any other regulating device known in the art. Combustion air can be provided to housing 12 by forced circulation, natural draft, a combination thereof, or in any other manner employed in the art.

The burner wall 16 is preferably constructed of a high temperature refractory burner tile material. However, it will be understood that the burner wall 16 could alternatively be formed of or provided by the furnace floor, a metal band, a refractory band, or any other material or structure which is capable of (a) providing an acceptable combustion air flow orifice (i.e., passageway) into the fired heating system and (b) withstanding high temperature operating conditions.

The inventive burner 10 can be installed, for example, through a floor or wall 38 of a boiler, fired heater, furnace or other fired heating system 40. Consequently, the forward (discharge) end 20 of burner wall 16 is in communication with the interior 42 of the fired heating system 40 in which combustion takes place. As a result of the combustion process, the interior 42 of the fired heating system 40 will contain inert combustion product gases (i.e., flue gas) 44. An insulating material 46 will also typically be secured to the interior surface of the floor or wall 38 outside of the burner wall 16.

The burner wall 16 and the air flow passageway 22 extending therethrough will preferably have round (circular) cross-sectional shapes. However, it will be understood that the cross-sectional shapes of the burner wall 16 and the air flow passageway 22 can alternatively be square, rectangular, oval, or generally any other shape desired.

The fuel discharge tip assembly 26 used in the inventive burner 10 preferably comprises a fuel discharge ring 30 which is positioned rearwardly of the forward discharge end 20 of the burner wall 16 and outside of the air flow passageway 22. Although a “ring” may typically be thought of as having a circular shape, the “fuel discharge ring” referred to herein and in the claims, unless otherwise expressly specified or limited, can be circular, square, rectangular, oval, or any other desired shape.

In most cases, it will be preferred that the shape of the fuel discharge tip 30 correspond to the lateral cross-sectional shape of the burner wall 16, or at least the forward end 20 thereof. In addition, the fuel discharge ring 30 will preferably have an inside diameter, or other inside dimensions in the case of a square, rectangular, oval, or other non-circular burner, which is/are greater than or equal to the outside diameter or other outer dimensions of the discharge end 20 of the burner wall 16.

The fuel discharge ring assembly 26 preferably also comprises: a fuel supply manifold 48; a fuel supply line (not shown) which supplies a gas or liquid burner fuel to the fuel manifold 48; and one or more (preferably a plurality of) fuel riser lines 50 which extend from the fuel supply manifold 48 to the fuel discharge ring 30.

When the inventive burner 10 is installed in the fired heating system 40, the fuel manifold 48 of the fuel discharge ring assembly 26 is preferably positioned outside of the floor or wall 38 of the fired heating system 40. The fuel riser lines 50 of the ring assembly 26 can extend from the fuel supply manifold 48, which is positioned outside of the heating system 40, to the fuel discharge ring 30 in the interior 42 of the heating system 40 either (a) through a radially extending refractory base which can be formed on and as part of the burner wall 16, (b) through the layer of insulating material 46 which is secured to the interior surface of the floor or wall 38 of the heating system 40 outside of the burner wall 16, or (c) through a gap 52 between the base of the burner wall 16 and the surrounding layer of insulating material 46.

Although a plurality of riser lines 50 are shown in FIGS. 1-4, it will be understood that a single riser line 50 can alternatively be used in the fuel discharge ring assembly 26. However, in order to provide a more equalized discharge of fuel around the entire circumference of the fuel discharge ring 30, the fuel discharge ring assembly 26 will preferably comprise at least 2, more preferably comprise at least 3, and most preferably at least 4, riser line connections 54 which are evenly spaced around the fuel discharge ring 30.

Also, the fuel discharge ring assembly 26 will preferably further comprise an outer protection sleeve 56 which surrounds the riser lines 50. The outer protection sleeve 56 preferably extends longitudinally from the furnace wall attachment flange 58 of the burner 10 to, or proximately to, the fuel discharge ring 30.

The fuel discharge ring 30 preferably entirely surrounds or substantially surrounds (i.e., extends from at least 95% to 100% of the entire distance around) the air flow passageway 22 of the burner wall 16. The fuel discharge ring 30 preferably has either one fuel discharge slot 60 (see alternative discharge ring 36 shown in FIG. 5) or a plurality of fuel discharge slots, ports or other openings 62 which is/are formed through the forward surface 64 of the fuel discharge ring 36 or 30 such that the slot or the plurality of other openings 60 or 62 substantially surround(s) or entirely surround(s) the air flow passageway 22. The plurality of fuel discharge openings 62, if used, will preferably be a plurality of round holes which are spaced from about 0.5 to about 200 diameters apart.

The size and orientation of the fuel discharge slot 60 or the plurality of other openings 62 and the fuel pressure supplied to the fuel discharge ring 30 or 36 are preferably such that the gas or liquid burner fuel is discharged from the slot 60 or other openings 62 in free jet flow outside of the burner wall in a direct or angled forward direction such that the ejected fuel flows along any desired straight or curving forward path to a combustion zone 66 which begins at or proximate to (i.e., within from 0 to +0.5 inches of) the forward end 20 of the burner wall 16. The fuel discharge slot 60 or plurality of other openings 62 is/are preferably oriented such that the fuel is ejected toward the outer edge 68 of the forward end 20 of the burner wall 16.

As the fuel ejected from the fuel discharge ring 30 or 36 travels toward the combustion zone 66 through the flue gas 44 in the interior 44 of the fired heating system 40, Internal Flue Gas Recirculation (IFGR) occurs wherein an amount of inert flue gas mixes with and conditions the ejected fuel. This conditioning of the fuel with inert flue gas slows the burning of the fuel in the combustion zone 66, thus reducing NOx production by lowering the peak temperature of the burner flame. In addition, IFGR mixing is further enhanced significantly by the momentum of the combustion air (or other oxygen-containing gas) exiting the forward discharge opening 24 of the burner wall 16 which pulls additional flue gas into the fuel and into the combustion zone 66.

To further promote the entrainment and mixing of the flue gas with the fuel ejected from the fuel discharge ring 30 or 36, the inventive burner 10 preferably includes one or more exterior impact structures positioned at least partially in the flow path of the fuel ejected from the fuel discharge ring 30 or 36. Each impact structure can generally be any type of obstruction which will decrease the flow momentum and/or increase the turbulence of the fuel stream sufficiently to promote flue gas entrainment and mixing while allowing the resulting mixture to flow on to the combustion zone 66.

In this regard, the burner wall 16 employed in the inventive burner 10 is preferably formed to provide a tiered exterior shape wherein the outer diameter of the base 70 of the burner wall 16 is broader than the outer diameter of the forward end 20 thereof and the exterior of the burner wall 16 includes one or a series of surrounding, spaced apart, impact ledges. By way of example, the outermost impact ledge of the burner wall 16 is defined by the outer edge 68 of the forward end 20 of the burner wall 16. At least one additional impact ledge 72 is then positioned around the exterior of the burner wall 16 between the fuel discharge ring 30 and the forward end 20 of the burner wall 16. The forward end 20 of the burner wall 16, which surrounds the forward air discharge opening 24, also forms a flame stabilization ledge for the combustion zone 66 of the inventive burner 10.

IFGR and flame stability are additionally increased in the inventive burner 10 by the formation of a plurality of ports, slots, or other openings 62, or of a single slot 60, in the fuel discharge ring 30 or 36, as discussed above, which substantially surround(s) or entirely surround(s) the air flow passageway 22. As also indicated above, when a plurality of discrete ports or slots 62 are used, the ports or slots 62 will preferably be spaced close together (i.e., preferably only from about 0.5 to about 200 port diameters or slot widths apart).

Consequently, as compared to the prior use of a plurality of individual fuel ejection tips, the inventive fuel discharge ring 30 or 36 significantly increases the total effective available tip area, thus allowing either (a) the use of a significantly greater number of ports 62 which are positioned closer together or (b) the use of a single surrounding fuel ejection slot 60 or a plurality of slots that are spaced only a short distance apart. These port or slot arrangements and reduced spacing provide an even greater degree of flue gas entrainment and flame stability.

To also enhance the equalization of air flow over the entire cross-section of the passageway 22 and/or change the shape of the flame if desired, a swirler 74 of the type commonly used in burners can optionally be positioned in the air flow passageway 22.

In addition to providing reduced peak flame temperatures and lower NO_(x) levels using IFGR as discussed above, the inventive burner 10 also achieves further flame temperature and NO_(x) level reductions by providing staged fuel operation in the combustion zone 66. By ejecting the fuel outside of the burner wall 16 into the exterior base portion 76 of the air flow discharged from the outer end 20 of the burner wall 16, the inventive burner 10 causes the combustion zone 66 to have (a) an outer surrounding fuel rich combustion region 78 and (b) an interior fuel lean combustion region 80.

In the outer fuel rich region 78 of the combustion zone 66, combustion occurs in an excess fuel to air ratio. In the inner lean combustion region 80, on the other hand, combustion occurs in an excess air to fuel ratio.

Also, it will be understood that further reduction in NO_(x) emissions can be achieved in the inventive burner and method by optionally including the additional use of (a) external flue gas recirculation, (b) steam and/or inert injection into the combustion air stream, (c) steam and/or inert injection into the combustion fuel stream, (d) flameless combustion, (e) one or more additional fuel ejection ring(s) or tips for further staged fuel operation, and/or (f) alternative port drillings to achieve staged combustion.

When operating the inventive burner 10 for combustion of a gas or liquid burner fuel in the fired heating system 40, air or other oxygen-containing gas is delivered through the flow passageway 22 surrounded by the burner wall 16. At the same time, a flow of the burner fuel is discharged forwardly, preferably in free jet form, from the fuel discharge ring 30 or 36 such that the flow of burner fuel is received in the combustion zone 66. Preferably, the free jet flow of burner fuel from the fuel discharge ring 30 or 36 is ejected directly toward the outer edge 68 of the forward end 20 of the burner wall 16.

As the flow of burner fuel is discharged from the fuel discharge ring 30 or 36, the flow preferably has a lateral cross-sectional shape which (a) substantially surrounds the flow passageway 22 and (b) corresponds to the outer lateral cross-sectional shape of the forward end 20 of the burner wall 16.

An alternative embodiment 100 of the inventive burner is illustrated in FIGS. 6 and 7. The structure and operation of the inventive burner 100 are substantially the same as the inventive burner 10 except that the inventive burner 100 is a flat flame burner wherein (a) the burner wall 116 and the air flow passageway 126 extending therethrough have a wide, flatter, rectangular shape, (b) the fuel discharge ring 30 of burner 10 is replaced with a T-bar ejector 130 having an elongate ejection tube or other conduit 132 which extends laterally adjacent to and across the exterior of the flat side 125 of the burner wall 116, (c) the burner 100 preferably does not include a burner fuel manifold, and (d) the T-bar ejector preferably has only a single fuel riser 134 which extends to the middle of the lateral ejection conduit 132.

The T-bar ejector 130 preferably has either a single elongate slot or a plurality of ports, slots or other openings 135 which extend(s) along at least most of the length of the forward surface 136 of the lateral ejection conduit 132, preferably from or proximately from one end 138 to or proximately to the other end 140 of the lateral conduit 132. Where a plurality of slot openings or circular port openings 135 are used, the openings are preferably only spaced from about 0.5 to 200 diameters or slot widths apart.

The single slot, or at least most, preferably all, of the plurality of slots or other openings, 135 provided in the lateral ejection conduit 132 is/are preferably oriented to eject the burner fuel toward the laterally extending outer edge 142 of the forward end 144 of the burner wall 116 on the flat side 125 of the burner. At least one additional impact ledge 146 is preferably also provided or formed in the exterior of the burner wall 116 between the forward outer edge 142 and the fuel ejection conduit 132.

Thus, the present invention is well adapted to carry out the objectives and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments and steps have been described for purposes of this disclosure, the invention is not limited in its application to the details of the preferred embodiments and steps. Numerous changes and modifications will be apparent to those of ordinary skill in the art. Such changes and modifications are encompassed within this invention as defined by the claims. In addition, unless expressly stated, the phraseology and terminology employed herein are for the purpose of description and not of limitation. 

What is claimed is: 1-10. (canceled)
 11. A burner apparatus comprising: (a) a burner wall having a combustion zone projecting from or proximately from a forward end of said burner wall, wherein said burner wall surrounds a flow passageway for air or other oxygen-containing gas which extends longitudinally through said burner wall, said flow passageway has a longitudinally forward discharge opening at said forward end of said burner wall, and said flow passageway has at least one side at said forward discharge opening which is substantially flat and (b) an elongate fuel discharge conduit which extends laterally outside of said one side of said flow passageway and is positioned longitudinally rearward of said forward end of said burner wall for discharging a burner fuel, wherein said elongate fuel discharge conduit includes either (i) a plurality of fuel discharge openings which extend along at least most of said elongate fuel discharge conduit and are oriented in a direct or angled forward direction to deliver said burner fuel outside of said burner wall to said combustion zone during operation or (ii) a single fuel discharge slot which extends along at least most of said elongate fuel discharge conduit and is oriented in a direct or angled forward direction to deliver said burner fuel outside of said burner wall to said combustion zone during operation.
 12. The burner apparatus of claim 11 wherein said elongate fuel discharge conduit includes said plurality of fuel discharge openings and said plurality of fuel discharge openings are round holes spaced from about 0.5 to about 200 diameters apart.
 13. The burner apparatus of claim 11 wherein: said forward end of said burner wall has a laterally extending outer edge on said one side of said flow passageway; said elongate fuel discharge conduit includes said single fuel discharge slot; and said single fuel discharge slot is oriented to eject said burner fuel toward said laterally extending outer edge of said forward end of said burner wall.
 14. The burner apparatus of claim 13 wherein said burner wall further includes an outer fuel impact ledge which is positioned between said elongate fuel discharge conduit and said laterally extending outer edge of said forward end of said burner wall.
 15. The burner apparatus of claim 11 wherein: said forward end of said burner wall has a laterally extending outer edge on said one side of said flow passageway; said elongate fuel discharge conduit includes said plurality of fuel discharge openings; and at least a portion of said plurality of fuel discharge openings are oriented to eject said burner fuel toward said laterally extending outer edge of said forward end of said burner wall.
 16. The burner apparatus of claim 15 wherein said burner wall further includes an outer fuel impact ledge which is positioned between said elongate fuel discharge conduit and said laterally extending outer edge of said forward end of said burner wall.
 17. The burner apparatus of claim 11 wherein said elongate fuel discharge conduit is positioned outside of said burner wall.
 18. A method of operating a burner comprising the steps of: (a) delivering an oxygen-containing gas through a flow passageway surrounded by a burner wall, said burner wall having a longitudinal axis which extends through said flow passageway, said flow passageway having a longitudinally forward discharge opening at a forward end of said burner wall, and said forward end of said burner wall having an outer lateral shape, wherein a combustion zone projects forwardly from or proximately from said forward end of said burner wall, and (b) discharging a flow of burner fuel forwardly from a fuel discharge ring such that said flow of burner fuel is received in said combustion zone, wherein said fuel discharge ring is positioned outside of said flow passageway and longitudinally rearward of said forward end of said burner wall and said flow of burner fuel, as it is discharged from said fuel discharge ring, has a lateral cross-sectional shape which substantially surrounds said flow passageway and corresponds to said outer lateral shape of said forward end of said burner wall.
 19. The method of claim 18 wherein said fuel discharge ring includes a plurality of fuel discharge openings substantially surrounding said flow passageway from which said flow of burner fuel is discharged.
 20. The method of claim 19 wherein said plurality of fuel discharge openings are round holes spaced from about 0.5 to about 5 diameters apart.
 21. The method of claim 19 wherein: said forward end of said burner wall has an outer edge and at least a portion of said plurality of fuel discharge openings eject said burner fuel toward said outer edge of said forward end of said burner wall.
 22. The method of claim 18 wherein said fuel discharge ring is circular.
 23. A burner apparatus comprising: (a) a burner wall having a combustion zone projecting forwardly from or proximately from a forward end of said burner wall, wherein said burner wall surrounds a flow passageway for air or other oxygen-containing gas which extends longitudinally through said burner wall and said flow passageway has a longitudinally forward discharge opening at said forward end of said burner wall and (b) a fuel discharge structure which is positioned outside of said flow passageway for discharging a burner fuel, said fuel discharge structure substantially surrounding, laterally, said flow passageway, wherein said fuel discharge structure includes either (i) a plurality of fuel discharge openings which substantially surround said flow passageway and are oriented in a direct or angled forward direction to deliver said burner fuel outside of said burner wall to said combustion zone during operation or (ii) a single fuel discharge slot which substantially surrounds said flow passageway and is oriented in a direct or angled forward direction to deliver said burner fuel outside of said burner wall to said combustion zone during operation.
 24. The burner apparatus of claim 1 wherein said fuel discharge structure is a fuel discharge ring which substantially surrounds, laterally, said flow passageway.
 25. The burner apparatus of claim 24 wherein said fuel discharge ring is longitudinally rearward of said forward end of said burner wall.
 26. The burner apparatus of claim 25 wherein said fuel discharge ring includes said plurality of fuel discharge openings and said plurality of fuel discharge openings are round holes spaced from about 0.5 to about 5 diameters apart.
 27. The burner apparatus of claim 25 wherein said burner wall has a circular cross-sectional shape and said fuel discharge ring is circular.
 28. The burner apparatus of claim 25 wherein: said forward end of said burner wall has an outer edge; said fuel discharge ring includes said plurality of fuel discharge openings; and at least a portion of said plurality of fuel discharge openings are oriented to eject said burner fuel toward said outer edge of said forward end of said burner wall.
 29. The burner apparatus of claim 28 wherein said burner wall further includes an outer fuel impact ledge which is positioned between said fuel discharge ring and said outer edge of said forward end of said burner wall and which surrounds said burner wall.
 30. The burner apparatus of claim 23 wherein: said forward end of said burner wall has an outer edge; said fuel discharge structure includes said single fuel discharge slot; and said single fuel discharge slot is oriented to eject said burner fuel toward said outer edge of said forward end of said burner wall.
 31. The burner apparatus of claim 30 wherein said fuel discharge structure is a fuel discharge ring which substantially surrounds, laterally, said flow passageway.
 32. The burner apparatus of claim 31 wherein said fuel discharge ring is longitudinally rearward of said forward end of said burner wall.
 33. The burner apparatus of claim 32 wherein said burner wall further includes an outer fuel impact ledge which is positioned between said fuel discharge ring and said outer edge of said forward end of said burner wall and which surrounds said burner wall.
 34. The burner apparatus of claim 23 wherein said fuel discharge structure is a fuel discharge ring positioned outside of said burner wall.
 35. The burner apparatus of claim 34 further comprising a plurality of delivery risers which deliver said burner fuel to said fuel discharge ring.
 36. The burner apparatus of claim 35 further comprising an outer sleeve, different from said burner wall, which surrounds said delivery risers.
 37. The burner apparatus of claim 23 wherein said burner fuel comprises a gas fuel.
 38. The burner apparatus of claim 23 wherein said burner fuel comprises a liquid fuel. 